Roofing Calculator

Roofing is measured in squares, where one square equals 100 square feet of roof surface. The most important insight this calculator provides is that the actual roof surface area is always larger than the building footprint because of pitch. A flat low-pitch (1/12) roof adds almost nothing, while a steep 12/12 pitch adds about 41% more surface than the footprint. That difference directly translates into material quantities, labor time, and cost — a 2,000-square-foot footprint with a 12/12 pitch actually has about 2,820 square feet of roof to cover.

Standard three-tab asphalt shingles come 3 bundles per square. Architectural (dimensional) shingles — now the most common choice in the US — also typically run 3 bundles per square, but always check packaging because premium products vary. Add 10–15% waste for a simple gable roof, and 15–20% for hip roofs, dormers, and roofs with multiple intersecting planes. Valleys and hips consume extra material for each additional cut, and ridge cap shingles are separate from the field shingles — add one bundle per 35 linear feet of ridge and hip.

Roofing underlayment is required under all asphalt shingles and is sold by the square. Drip edge metal runs the full perimeter and starter strip runs the eaves and rakes — these materials are often overlooked when budgeting but add up quickly on larger roofs. If your existing deck boards show any rot or soft spots, budget for replacement before pricing shingles. Discovering bad decking after the old shingles are stripped is the most common source of roofing cost overruns — it's far cheaper to inspect and price boards before the project begins than to find out mid-tearoff.